1. Field of the Invention
The invention relates to a process for the purification of adenine, especially of crude synthetic adenine, which optionally contains 9-phenyladenine and/or other byproducts.
2. Background Art
Adenine (6-aminopurine) plays an important role in nature as a component of nucleic acids, adenosine phosphates and other essential compounds. In addition to a direct pharmaceutical application ("vitamin B.sub.4 ") and use in biochemical research, it is used, for example, as initial material for the production of pharmaceutical active ingredients (see, e.g., West Germany OS 2,804,723).
An important process for the production of adenine (European Published Patent Application No. 0,045,503; British Patent No. 1,518,784) starts from malonitrile, which is coupled with diazotized aniline to phenylazomalonitrile. The latter is reacted with ammonia and formamide to 4,6-diamino-5-phenylazopyrimidine which is cleaved reductively to 4,5,6-triaminopyrimidine and aniline. Adenine finally is obtained with formamide from the triaminopyrimidine. But the process takes place with the formation of byproducts. As impurities, the crude adenine formed typically contains about 1 percent of 9-phenyladenine and about 2 to 5 percent of a brown substance of unknown constitution. To obtain a pure product with a content of over 99 percent, it previously was necessary to recrystallize the crude adenine, optionally in the form of the sulfate, using activated carbon several times. This type of purification is not only very tedions and time-consuming, but also causes considerable losses of substance; its yield is not over 75 percent.